BOGOTA (Reuters) - Former Colombian President Alvaro Uribe's political movement chose economist Oscar Ivan Zuluaga on Saturday as its candidate for presidential elections in May, a vote he looks set to contest echoing Uribe's tough stance against leftist guerrillas.

A businessman and former finance minister under Uribe, Zuluaga, 54, would be a key opponent of President Juan Manuel Santos if the incumbent runs for another term, a decision he must announce by late November.

Zuluaga's anointing as the 'Uribista' candidate gives him instant political weight through Uribe's continued popularity resulting from success in beating back the FARC and ELN guerrillas with U.S. support during his 2002-2010 presidency.

In the 2010 elections, Santos ran as an Uribe successor after serving as his defense minister. But as president, Santos changed course in the fight against the guerrillas by starting peace talks with the leftist FARC while keeping up military strikes against them.

The year-old talks have progressed slowly, with only a partial agreement on one of the five points on the agenda which include the rebels' participation in politics, but neither side has walked away from the talks so far.

"The country will recover what it should never have lost - its freedom," Zuluaga said in a speech after he was announced as the movement's candidate. "I invite (Santos) to run for re-election to beat him at the polls through the ideas of Uribism."

Uribe has kept a high profile since leaving office, commenting on TV news on current affairs and through constant, scathing criticism of Santos delivered on Twitter, accusing him of frittering away hard-won security gains.

"This act is the beginning of the repeal of the voice they have given to terrorism in Colombia, contrary to what was promised when they came to the polls," Uribe said, referring to the peace process Santos initiated.

The FARC and their smaller counterpart, the ELN, which are estimated to have 8,000 and 3,000 fighters respectively, have been fighting the government in a 50-year conflict that started as a peasant revolt and has killed more than 200,000.

Santos, who is widely expected to run for a second term, has said he wants the basic policies of his government to continue after next year's election, including negotiations with the FARC. Should he run, he will be able to point to a record of steady-handed economic management with low inflation and buoyant growth.

Due to constitutional rules, Uribe, a 61-year-old trained lawyer, cannot run for another term in office, but he announced last month he would seek election to the senate.